This pet is only purchasable from Nat Pagle at a level 3 Fishing Shack. Players must have the Good Friends reputation with Nat Pagle in order to buy the Sea Calf.

The Fishing Shack can be built and unlocked at level 94. Upgrading it to level 3 requires the achievement "Draenor Angler" and a level 3 garrison.

Once the Fishing Shack is level 3, players must recruit Nat Pagle as a follower through a short quest chain. After he becomes a follower, assigning him to "work" at the Fishing Shack will allow players to catch Lunker-fish without the aid of a special lure.

To earn Nat's Lucky Coin (and reputation with Pagle), players will need to fish for special fish called Lunkers. Turning these in will reward friendship with Nat Pagle as well as one coin each turn in.

Finally got this pet today. Just fished up and down the east coast of Spires of Arak to get the 50 lunkers. Took some advice from the Wowhead comments, and focused on pools vs. open sea fishing. With a Tentacled Hat + Ephemeral Fishing Pole + Worm Supreme + Fishing enchant to gloves, had 1105 fishing. Averaged about a 7% fish rate on the lunkers.

My only issue with this pet is her size - way too tiny for a sea calf even tho in Nature the males tend to be the bigger ones...still would be nice to have the sea calf a bit bigger upon summoning. Just a tip if you can't seem to find one on your server, the Brazilian server, Azralon, seems to have at least 7 up at any one time. So far I have seen 4 different breeds: P/B, B/B, S/B, H/B

I confirmed this by copying my fishing character over to the patch 6.1 PTR and when I checked what Nat was selling, there it was! So it looks like the bug that kept this pet from showing up is finally fixed! =)

The notes here say that it sold by Nat Pagle in the garrison, but it's not currently for sale. I've unlocked the level 3 fishing shack and can buy everything else he's supposed to sell (drinking hat, draenic fishing pole, land shark pet, fishing journal, crimson water strider mount), but this isn't showing up. Wowhead doesn't list how to obtain it either.